Socrates took 93.3 percent of party member votes, putting him firmly at the helm ahead of elections likely to be called within weeks after he resigned Wednesday.
All five opposition parties voted Wednesday against his minority government's fourth programme in a year of spending cuts and tax hikes aimed at averting an EU-IMF bailout to help Lisbon meet debt repayment obligations.
The number of votes given to Socrates by about 32,000 party members in the election on Friday and Saturday was higher than at his win at the previous leadership poll in 2009, the party said in a statement.
The result is to be ratified at the party's April 8-10 congress.
Socrates has been prime minister since 2005. He resigned when the austerity plan was rejected, saying he could not govern without support.
Lisbon is trying to bring its public deficit down from a record 9.3 percent of GDP in 2009 to 4.6 percent this year.
Socrates has insisted Portugal does not need a financial rescue package but analysts say it is only a matter of time before it will need help along the lines of packages granted to Greece and Ireland.